Question

Explain with the help of a balanced equation the brown ring test for nitric acid.

Answer 1

Procedure:

1. Add freshly prepared saturated solution of iron (II) sulphate to the aq. solution of nitric acid.
2. Now add conc. sulphuric acid carefully from the sides of the test tube so that it does not fall dropwise in the test tube.
3. Cool the test tube in water.
4. A brown ring appears at the junction of the two liquids.

 

Reaction:

\[\ce{6FeSO4 + 3H2SO4 + 2HNO3 -> 3Fe2(SO4)3 + 4H2O + 2NO}\]

\[\ce{FeSO4 + NO -> \underset{a brown compound]}{\underset{[Nitroso ferrous sulphate,}{FeSO4*NO}}}\]